Heart disease is the leading killer of Americans, and the lifetime risk among healthy Americans remains dangerously high.

Despite the plethora of data on what contributes to heart disease, no study has calculated the lifetime risk of the disease for the average adult. So Northwestern University cardiologist John Wilkins and his colleagues pooled data from five long-running studies of U.S. heart health, and used them to calculate disease risks at various ages, and for people with different combinations of risk factors. Together, the data cover tens of thousands of people who were monitored and followed up for cardiovascular events for various periods between 1964 and 2008.

Previous studies have calculated heart disease risk over short time intervals of just a few years, or assessed the lifetime risk of developing a single cardiovascular condition, such as congestive heart failure. The latest analysis considers the lifetime risk for all cardiovascular diseases, a category that includes coronary artery disease (whose symptoms are most often heart attack and angina) along with strokes, congestive heart failure, and more.

And the results are sobering. At age 45, the lifetime heart disease risk is 60.3% for men and 55.6% for women, according to the researchers. That means that, on average, a 45-year-old man without heart disease can expect that he will develop the disease at some point in his life with 60.3% probability. Or, alternatively, that three out of five men without heart disease at age 45 will develop the condition at some point in their lives. Risks are higher for men than for women at all ages, according to the study, which was published in the Journal of the American Medical Association.

These lifetime risks are also strongly linked to known heart risk factors such as smoking, diabetes, high blood pressure, and high cholesterol. The greater the number of risk factors, the higher the probability that a person will eventually get heart disease.

But even for people with none of the conditions that can endanger the heart, the chances of developing trouble cardiovascular disease from age 45 onward is still over 30% – which means more than three out of ten people with no reason to worry about heart disease in middle-age may succumb to those conditions at some point in their lives. With such high probabilities, few are spared: even people with relatively low risk may suffer from heart problems eventually, although they typically live longer and healthier lives before developing the first symptoms sets in. Wilkins and his coauthors find that people with an optimal risk-factor profile at age 45 have, on average, eight to 14 more years of heart disease-free life than people with two or more risk factors in early middle age. So while the risk can’t be brought down to zero, the study suggests that it does help to manage risk factors such as not smoking, controlling blood pressure, and maintaining healthy blood sugar and cholesterol levels.

It’s hardly surprising that Americans are at high risk of developing heart disease, but the sobering reality of just how great that risk is may reinforce public health messages to avoid symptoms and potentially avoid the disease.